U.S. patent number 6,806,607 [Application Number 10/321,764] was granted by the patent office on 2004-10-19 for electric motor.
This patent grant is currently assigned to Johnson Electric S.A.. Invention is credited to James Ching Sik Lau.
United States Patent |
6,806,607 |
Lau |
October 19, 2004 |
Electric motor
Abstract
A miniature PMDC motor 10 has a permanent magnet stator
comprising two arcuate ceramic magnets 20 fitted to a can-like
housing 11 and circumferentially separated by interdisposed rubber
magnets 21 wedging or nipping the ceramic magnets 20 in place
within the housing 11 without the use of circumferential magnet
stops formed in the side of the housing.
Inventors: |
Lau; James Ching Sik (Hong
Kong, CN) |
Assignee: |
Johnson Electric S.A. (La
Chaux-de-Fonds, CH)
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Family
ID: |
9927781 |
Appl.
No.: |
10/321,764 |
Filed: |
December 18, 2002 |
Foreign Application Priority Data
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Dec 18, 2001 [GB] |
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0130152 |
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Current U.S.
Class: |
310/154.01;
310/154.03; 310/154.06; 310/154.07; 310/154.21; 310/154.28;
310/154.36; 310/254.1 |
Current CPC
Class: |
H02K
1/17 (20130101); H02K 23/04 (20130101); Y10T
29/49075 (20150115); Y10T 29/49009 (20150115); Y10T
29/49012 (20150115) |
Current International
Class: |
H02K
1/12 (20060101); H02K 1/17 (20060101); H02K
23/02 (20060101); H02K 23/04 (20060101); H02K
021/26 (); H02K 021/38 (); H02K 023/04 () |
Field of
Search: |
;310/40MM,154,156,254 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Patent Abstracts of Japan, vol. 007, No. 258, Nov. 17, 1983
(Japanese Publication No. 58144565, published Aug. 27, 1983). .
Patent Abstracts of Japan, vol. 017, No. 535, Sep. 27, 1993
(Japanese Publication No. 05146101, published Jun. 1,
1993..
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Primary Examiner: Nguyen; Tran
Assistant Examiner: Aguirrechea; J.
Attorney, Agent or Firm: Birch, Stewart, Kolasch &
Birch, LLP
Claims
What is claimed is:
1. A miniature electric motor comprising: a wound rotor; a
permanent magnet stator disposed about the rotor; a housing
supporting the permanent magnet stator; wherein the permanent
magnet stator comprises at least two arcuate ceramic magnets
separated circumferentially by rubber magnets.
2. The motor of claim 1 wherein the ceramic magnets are located at
the poles of the stator.
3. The motor of claim 1 wherein the rubber magnets have a magnetic
charge profile in which the magnetic field varies across the rubber
magnets.
4. The motor of claim 1 wherein the ceramic magnets are glued to
the housing.
5. The miniature electric motor of claim 1 wherein the housing has
no holes in a circumferential wall supporting the magnets.
Description
This nonprovisional application claims priority under 35 U.S.C.
.sctn. 119(a) on Patent Application No. 0130152.2 filed in Great
Britain on Dec. 18, 2001, which is herein incorporated by
reference.
This invention relates to electric motors and in particular, to
miniature electric motors having a permanent magnet stator.
PMDC motors are very common and have many uses and applications.
Some applications require motors with a relatively high power with
small physical size while some applications require the motor to
have low cogging.
Cogging can be reduced by shaping the rotor poles and/or the stator
poles. As the stator is a permanent magnet, the shaping of the
stator poles means shaping the magnets or the magnetic field which
can be shaped during the charging of the magnets. This is usually
only possible with ring magnets but ceramic ring magnets are very
expensive and rubber ring magnets are not as strong.
When using ceramic magnets, it is usual to use two arcuate ceramic
magnets which are circumferentially located with respect to the
can-like housing by stops which engage one longitudinal side of
each magnet and one or more springs located between and bearing
against the other longitudinal edge of the magnets, pressing the
magnets into contact with the stops.
A similar arrangement is used with four arcuate magnets and two
steps of stops.
Once installed in the housing, the magnets are charged. However,
the gap between the ceramic magnets represents a gap in the
magnetic field of the stator and any shaping of the magnetic field
must take this gap into consideration.
The rubber ring magnet, on the other hand, requires no springs and
no stops pressed into the wall of the housing. The magnet is held
in place by the magnet itself which expands when it is charged
resulting in a housing without side openings. However, there is a
need for a housing without side openings which supports a more
powerful magnet such as a ceramic magnet.
Accordingly, the present invention provides a permanent magnet
motor having a cylindrical housing containing a permanent magnet
stator and a wound rotor, wherein the permanent magnet stator
comprises at least two arcuate ceramic magnets circumferentially
spaced by rubber magnets. The present invention also provides a
method of making such a motor.
BRIEF DESCRIPTION OF THE DRAWINGS
One preferred embodiment will now be described, by way of example
only, with reference to the accompanying drawings, in which:
FIG. 1 illustrates a permanent magnet direct current electric motor
according to the preferred embodiment of the present invention;
FIG. 2 is a longitudinal cross-section of the stator of the motor
of FIG. 1; and
FIG. 3 is a transverse cross-sectional view of the stator of FIG.
2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The motor shown in FIG. 1 is a miniature PMDC motor 10 having a two
pole permanent magnet stator. The stator comprises a cylindrical
can-like housing 11 surrounding the permanent magnets and
accommodating a wound rotor of which only a shaft 12 is visible.
One end is closed by a molded resin end cap 14 which supports motor
terminals 15, brush gear and a bearing. The other end of the
housing 11 also supports a bearing for the rotor shaft 12. Although
shown as having one open end and one closed end, the housing could
have two open ends, both of which are closed by separate end
caps.
The stator, more clearly shown in FIGS. 2 and 3, has two ceramic
arcuate magnets 20 placed inside the housing 11. There are no stops
formed in the housing to locate the magnets 20 circumferentially
with respect to the housing 11. A rubber magnet 21 is pressed into
each gap between adjacent longitudinal edges of the ceramic magnets
20. The rubber magnets 21 can be compressed to aid assembly but
once charged, the rubber magnets 21 swell, creating a firm
interference fit between the ceramic magnets 20 and the rubber
magnets 21 fixing the magnets 20, 21 to the housing 11.
The ceramic magnets 20 may be additionally supported by gluing the
magnets to the housing 11. The housing 11 may have a notch 16 at
one end for aligning the magnets 20, 21 within the housing 11
during assembly and subsequently, for aligning the end cap 14 with
the housing 11 so that the brushes are correctly aligned with the
magnets to ensure the correct commutation angle.
Although a two pole stator has been shown in the example, the
inventive concept can be applied to permanent magnet stators
generally having two or more poles and is particularly suited to
four pole stators.
The motor thus constructed has a stator with a continuous magnetic
field similar to that provided by a ring magnet but with higher
energy ceramic magnets at the pole centres and rubber magnets at
the interface between the poles allowing shape charging of the
stator. This method also allows for the simple fixing of arcuate
ceramic magnets to a motor housing and avoids the use of housing
deforming magnet stop wings punched into the side of the
housing.
The embodiment described above is given by way of example only and
various modifications will be apparent to persons skilled in the
art without departing from the scope of the invention as defined in
the appended claims.
* * * * *